Many underground metal mines remove large volumes of waste rock along with the metal values during the mining cycle. This occurs because these ore bodies occur in the form of thin beds or veins, the thickness of which is much smaller than the smallest practical size for entry headings necessary for mining operations. The resulting dilution of the ore values is very undesirable because it increases costs for handling and milling of the ores.
The underground metal mining industry has long sought an effective means of selectively mining or separating the ore values from waste during the mining cycle. Many attempts have been made to achieve this capability using various types of mechanical cutters and picks. These approaches have met with little success because of difficulties in gaining access to the vein beyond a short distance from the face in hard rock.
In order to cut hard rock in quarries and underground mines to mine veins, various mechanical devices have been used which use bits. However, these devices show severe wear when used in hard rock. Abrasive water jet designs have also been proposed for use in hard rock. However, such devices have been unable to make deep cuts because of significant energy losses and dispersion as the abrasive slurry moves away from the high pressure water nozzle. In addition, normal kerf cutters and high pressure water jet drills require excessively high pressure (50,000 psi) for cutting hard rock. Because of these high pressures, these devices tend to be unreliable. Usually, the most unreliable part is the swivel because the seals fail so readily under the pressures and rotation rates.
One prior art mining cutter using water jet pressure is disclosed in U.S. Pat. No. 4,280,735 (Lobbe). In this patent, a tool for a mineral winning machine is disclosed having a flat plate-like body with a bore containing a nozzle insert and a hard metal cutting region or blade. High pressure water is conveyed through the bore and nozzle insert to discharge as a jet which is directed to impinge against the mineral or coal face.
Another prior art water jet mining device is disclosed in U.S. Pat. No. 4,265,487 (Barker). According to the disclosure of this patent, a machine is provided in which a plurality of nozzle modules are mounted. Each nozzle module contains a high pressure water jet nozzle disposed to oscillate in a particular plane. The nozzle modules are oriented to cut in vertical and horizontal planes on the leading edge of the machine and the coal so cut is cleaved off by a wedge-shaped body.
Still another hydraulic cutting tool is disclosed in U.S. Pat. No. 4,240,664 (Mahyera et al). The device disclosed in this patent is designed for cutting kerfs in rocks and other hard formations by provision of divergent hydraulic jets in a cutter implement. The cutter implement cuts clearance for passage of the implement into the kerf being cut. The cutting implement includes a generally elongate nozzle housing with longitudinally spaced apart and transversely directed jet nozzles therein.
Disclosed in U.S. Pat. No. 4,119,160 (Summers et al) is an apparatus for water jet drilling of rocks including a nozzle. This nozzle is rotated and includes two outlets. One outlet is directed in a direction of movement of the nozzle while the other outlet is directed in an angle to this direction. In this manner, a cylindrical bore is drilled in the rock. A variety of other outlet designs is also disclosed in U.S. Pat. No. 3,796,371 (Taylor et al).
Disclosed in U.S. patent application Ser. No. 699,513 (now abandoned) is an abrasive water jet slot cutter including an elongate tube from which the water jet exits. Although this water jet slot cutter has proven especially effective, the collimated abrasive water jet cuts too narrow a kerf to permit the collimating tube to follow into the cut. Thus, in order to advance the kerf to the depths required in many mining applications, two parallel kerfs have to be cut and the intervening rock rib removed. Mechanically, this created the requisite clearance so that the collimator could be advanced in the kerf and to continue the cutting deeper into the rock. However, this was a continuous, two-step process which was unduly time consuming.